Many beam pumping units for extracting underground crude oil have an overground driving mechanism for driving a reciprocating piston pump in an oil well. The overground driving mechanism typically includes an alternating-current (AC) electric motor such as an induction motor or an asynchronous motor. In a beam pumping unit, a rotary motion provided by the output shaft of the AC electric motor is converted to a vertical reciprocating motion, also known as the nodding motion, to drive a polished rod for extracting underground oil.
In a conventional beam pumping unit, the conversion of the rotary motion of the output shaft of the AC electric motor to the vertical reciprocating motion utilizes, among other things, a gear speed reducer and a belt. The gear speed reducer and the belt convert a high-speed rotary mechanism to a low-speed rotary mechanism for producing the low-speed vertical reciprocating motion. The AC electric motor, the gear speed reducer, and the belt, produce large-enough torque to drive the load for extracting oil. The gear speed reducer and the belt, however, typically have a short life time and require expensive maintenance. Moreover, the AC electric motor usually receives control signals having a fixed frequency and a fixed voltage from its controller. Consequently, the torque produced by the AC electric motor cannot be adjusted according to, for example, a variation of the load, a variation of the oil level, etc.
In other conventional beam pumping units, a linear motor is used to drive the load for extracting oil. The linear motor's stator and rotor are unrolled so that instead of producing a torque (rotation), the linear motor produces a linear force along its length. But the linear motor is expensive and reduces its commercial value and wide usage in the industry.
Therefore, there is a need for an intelligent beam pumping unit that utilizes a relatively inexpensive direct drive motor to produce large-enough torque to drive the load for extracting underground objects, such as liquid, gas, or solid, adjusts the torque and speed of the motor to increase the amount of liquid or gas extracted, and reduces or eliminates the maintenance effort of the overground driving mechanism.